From what I understand, nothing that mitigates environment card/target damage will work on PW Tempest's power. The damage is not coming from an environment target, nor from an environment card. Mass Levitation doesn't affect it, nor does Mega Computer, nor does Environmental Allies. There's only one situation where that damage is negated/reduced due to anti-environment effects: using Setback's Wrong Place and Time to redirect the damage to Iron Legacy (who is "immune to damage from the environment"). Heck, even the Chairman's backside isn't immune to this damage when Setback redirects it to him (he's only immune to damage from environment cards). Your best bet is to have Captain Cosmic give Energy Bracers to Tempest. Between Tempest's Otherworldly Resiliance, Elemental Subwave Inducer, and up to 3 Energy Bracers (choose 3 of those 5), you can get the damage down to 0.
My favorite combos:
1. America's Greatest Legacy's Lead From the Front + Setback's High Risk Behavior (preferably x2) = complete removal of High Risk Behavior's disadvantage allowing you to go to crazy heights of bonus damage. Throw in Setback's Looking Up and you can get a crazy amount of Unlucky Tokens super fast, and then when the damage gets too high, you use Wrong Time and Place to start turning that token gain into damage (spend the 3 tokens you gain from Looking Up's power to power Wrong Time and Place to redirect the start of turn self-damage from Looking Up). This works particularly well when playing with Grandpa Legacy since he can use his power to make Setback gain three more Unlucky tokens (and another +2 to villain targets!) on Legacy's turn. Besides, Galvanize just makes Setback hit himself harder, costing extra tokens to redirect the damage. With sufficiently lucky draws, this combo gains +5.3 damage to villain targets each turn as well as hitting at least twice (thrice if you forfeit +2 damage) for 3 base damage. So, 5+7 damage the first turn you have the combo, then 11+13 the second turn, then 15+17 the third turn, then 19+21... And that's just with powers from two heroes (once you get the 4-card combo, of course).
2. (This one I found out from playing the video game version - I never thought to do it before!) Absolute Zero + Visionary's Twist the Aether = hilarity.
A lot of AZ's cards make him hit himself for a bunch of fire damage, allowing you to then deal that much cold damage to a foe. If you need healing, you can hit yourself with the cold blast, healing you more than you were hurt, but barely more than that. Twist the Aether changes this wonderfully.
Suddenly, instead of doing 10 fire damage to yourself which you turn into 12 healing causing you to gain 2 HP, you deal 13 cold damage to yourself which gives you 13 HP. Frost-bound Drain: Deal 1 target 4-5 cold damage and heal yourself for 4-6 HP. Hoarfire can become: deal 1 target 4 cold damage, regain 5 HP, regain 4 more HP, lose 1 HP and deal 1 target 3 cold damage (deal 7 damage, heal 8). Or, you can do it as, deal 1 target 4 cold damage, deal yourself 2 fire damage, deal that same target 4 cold damage, regain 4 HP, regain 4 HP (deal 8 damage, heal 6 HP). When you're really hurt, you use Thermal Shockwave to deal 2 targets 3 cold damage each and yourself 2 fire damage, which turns into 4 cold vs one of those targets you already hit. Then, you regain 12 HP, for a net gain of 10 HP and net damage of 10.
Then, use one of the one-shots at the same time as Thermal Shockwave, since it's a power. In that case, you'd heal for closer to 18, poissibly 25 if the cold damage that heals you counts as damage for the purposes of Thermal shockwave. It's absurd and hilarious and a lot of fun!
3. I haven't tried this one yet, but Super Scientific Tachyon + Parse's Updated Intel + Argent Adept's Arcane Cadence. You can sub in Nightmist's Astral Premonition for either Parse or AA, or just use Parse's Gauge if you want it to be a two-hero combo. Basically, don't leave Super Scentific Tachyon's experimentation to luck, leave it to SCIENCE! With the ability to play or discard the bottom two cards of any deck, it's kinda awesome.
4. Very specific, but... Legacy's Heroic Interception (or Ra's imbued flesh combo but that's slower) + Visionary's Brain Burn when fighting The Chairman. Hit him asap with Brain Burn while protected from the self-harm and suddenly, there are no thugs for the underbosses to play. This is preferably done on the first turn. I guess 10 damage isn't all that much, so a first turn Brain Burn is totally awesome even without the damage immunity, but with the damage immunity it becomes just totally ridiculous.
5. Omnitron-X's Singularity + Skyscraper's link cards. The downside to Skyscraper is that her link cards, while really easy to get out, are a bit harder to get into her trash. Having them in her trash isn't a big deal because she can get them back super fast with her Tiny base power. Omnitron-X's Singularity is powered by any number of equipment cards, with no requirement that they be Omni's. This seems like a great combo I have not yet tried. They really seem like a powerful combo, since Omni can really benefit from Sky's micro-assembler.